I did not bother. As a non American, I would probably get close to zero. But I am aware that slavery has been a part of human existence forever. Britain abolished it in 1833, but it goes way back. The ancient Greeks were revered for their wisdom and their philosophers, but their economies depended on the work of slaves. The great philosophers would not have been able to sit around thinking if it were not for the fact that they survived on the exploitation of slaves.

Slavery is so widespread throughout history that I am pretty sure that more human societies kept slaves than those that did not. The native people of my country, the Maori, kept slaves. Most primitive societies did. Some of the slavery has been very ugly, and sex slaves have been almost as common as general slaves. In fact, I suspect that the reason Homo sapiens has neanderthal genes is because neanderthal women were taken as slaves and used sexually.